1. Field of the Invention
The invention relates to an apparatus for providing isolation for a power supply. The invention also relates to providing a voltage multiplier function for the power supply. More specifically, the invention relates to the use of two out-of-phase signals in an arrangement of capacitors and diodes in order to provide both capacitive isolation and voltage multiplication for a DC-DC converter power supply.
2. Description of the Related Art
It is often necessary to have a voltage that is several orders of magnitude greater than a supply voltage. For example, a voltage doubler is commonly required to provide the necessary amount of voltage to a load.
Ideally, a power supply that supplies power to a load should be isolated from the drivers that are connected to the power supply. That is, isolation is desired in order to protect analog I/O lines from the voltage levels of other systems, which may cause failures when the I/O lines are connected to other systems which operate at elevated voltages.
Transformers are typically used to provide isolation for a power supply or a converter. However, transformers are typically large in size (due to the size of the magnetic elements within them) and are costly.
Charge pump devices can be used to obtain an output voltage that is greater than an input voltage; i.e., to provide a voltage amplification function. Conventional charge pump devices include a series of stages, with each stage including a capacitor and a switch. Each stage of the charge pump device boosts the magnitude of the voltage input to the stage by a voltage equal to the voltage swing of a two-phase signal applied to the capacitor in the stage.
At each stage, the capacitor will store an increased maximum voltage difference across its plates. For example, using a +12 volt supply, the capacitor in the first stage will store a charge proportional to 12 volts across its plates, the capacitor in the second stage will store a charge proportional to 24 volts across its plates, etc.
The magnitude of the voltage across the capacitor will determine its structure and size. The greater the amount of voltage that a capacitor can withstand, the greater the size of the capacitor, which leads to a larger and more expensive capacitor, and hence a larger and more expensive power supply.